Malicious Office (OOXML) / .XLSX — malware analysis report

Static analysis result for SHA-256 fac6013fabec2b01…

MALICIOUS

Office (OOXML) / .XLSX

87.7 KB Created: 2021-10-27 10:31:49 UTC Authoring application: Microsoft Excel 12.0000
MD5: e077723744d8f004a1a526094f1b5bec SHA-1: 70b272d0a2f8180ef553e5fc42dd14fa420f5f67 SHA-256: fac6013fabec2b010f20a2bc20162853e926aa1ebe3496775f1674ee52be97d6
182 Risk Score

Malware Insights

MITRE ATT&CK
T1059.005 Service Execution: Visual Basic T1204.002 Malicious File: User Execution

The sample contains Excel 4.0 macros that reassemble a payload. This payload executes 'mshta C:\ProgramData\fnsfunsfgrgnkjfsgnd.rtf', indicating an attempt to download and execute a second-stage payload from the specified path. The URLs extracted are likely related to the payload delivery mechanism.

Heuristics 4

  • Excel 4.0 macro sheet (1 sheet(s)) critical OOXML_XLM_MACROSHEET
    Spreadsheet contains an Excel 4.0 (XLM) macro sheet — XLM was a major Office malware vector during 2020-2022 and evaded many VBA-focused controls before Microsoft tightened XLM defaults. Even legitimate XLM use is rare in modern workbooks. The macro sheet is stored as XLSB/BIFF12 binary content, which many XML-only OOXML scanners miss.
  • XLM payload reassembled from CHAR()/split formulas critical OOXML_XLM_REASSEMBLED_PAYLOAD
    An Excel 4.0 macro sheet builds its payload inside the formula token stream by concatenating per-character CHAR() calls and string fragments, so no WinAPI name, shell command, or URL is ever contiguous in the .bin for a literal-bytes scan to find. Reassembling the formulas recovered download/execute API names, LOLBin commands (regsvr32/rundll32/mshta/wmic/powershell), or a payload URL — the de-obfuscated download-and-run kill chain.
  • URL reconstructed from XLM cell array (3 URLs) critical OOXML_XLM_CELL_ARRAY_URL
    Excel 4.0 macro sheet stages its payload URL across individual numeric cells (one ASCII charcode per cell) or inside an embedded HTA that uses VBScript Chr()/&-concat obfuscation. The reconstructed URL is invisible to literal-bytes URL extraction because it is never contiguous in the workbook stream. URLs were recovered by walking the BIFF12 record stream of every worksheet and macrosheet part and decoding RK/inline-string cells in both row-major and column-major order.
  • Embedded URL info EMBEDDED_URL
    One or more URLs were extracted from the document. The URL itself is not a detection — see the per-URL labels for which channel (macro, JS, link annotation, document body, ...) reached each URL.
    URL https://cdn.discordapp.com/attachments/908712469780889674/909803740146581514/irHfCekilljews.mkv
    • https://cdn.discordapp.com/attachments/908714245779247107/909805453951791115/qIAtTZTHXxEbOgCkilljews.mkv
    • https://cdn.discordapp.com/attachments/908712469780889674/909803789949759578/ATVQXjdkHCpZkilljews.mkv

Extracted artifacts 1

Files carved from inside the sample during analysis.

FilenameKindSourceSize
xlm_sheet_00.bin
4975a4af297cdcacfea51bf5839339e3f9e04dac46b2da35a82da1f666eb118c		 xlm-macrosheet OOXML XLM macro sheet: xl/macrosheets/sheet1.bin 4424 bytes

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